Does “thrull” as in the name of the Magic: the Gathering creature type etymologically come from “thrall”? If not, then where does the word come from? Does the word appear in earlier fantasy fiction?
The word "thrull" is not found in the Oxford English Dictionary. The OED is pretty good about noticing terms that are used even to describe fictional elements in science fiction and fantasy. (For example, it has citations for "vape" as a SF term meaning "vaporize" going back decades, to well before the word was use in connection with nicotine products.) So I think this can be relied upon as an indication that the term was not in circulation in SF and fantasy prior to the release of the Fallen Empires expansion set of Magic: The Gathering. (I will concentrate in my answer primarily on the Fallen Empires set from 1994, since it was as part of that set that the thrulls were named.)
When Fallen Empires came out, I built an all-black deck based around the thrull cards; it contained every unique card that even referenced the thrulls. I did some research at the time, reading the Wizards of the Coast's press statements and interviews with the developers, but none of them ever explicitly stated that "thrull" came from "thrall." Searching the Web in 2017, I still do not see any explicit confirmation of this fact.
However, it is hard to believe that the similarity in terms could have been just coincidental. The first (and primary) OED definition for thrall is (marked archaic or historical, but not obsolete):
- a. One who is in bondage to a lord or master; a villein, serf, bondman, slave; also, in vaguer use, a servant, subject; transf. one whose liberty is forfeit; a captive, prisoner of war.
b. fig. One who is in bondage to some power or influence; a slave (to something)
The key element of thralldom is being in the power of another party, and that is how Magic's thrulls began. The thrulls in Fallen Empires were explicitly disposable, first bred for sacrifice, created by Endrek Sahr of the Order of the Ebon Hand. One of the flavor texts for the Basal Thrull was
Initially bred for sacrifice, the Thrulls eventually turned on their masters, the Order of the Ebon Hand, with gruesome results. —Sarpadian Empires, vol. II
And on the Thrull Retainer card:
"Until the Rebellion, thrulls served their masters faithfully—even at the cost of their own lives." —Sarpadian Empires, vol. II
"The worst thing about being a mercenary for the Ebon Hand is having to wear a dead Thrull." —Ivra Jursdotter
"They gave their lives to strengthen the Order's armies, until they declined this honor in favor of joining the Thrull Rebellion." —Jherana Rure, Counter-Insurgency Commander
Many of the thrull and thrull-related cards included thrull sacrifice mechanics: Basal Thrull, Necrite, Mindstab Thrull, Armor Thrull, Thrull Retainer, Ebon Praetor, Tourach's Gate, Soul Exchange and the post-Fallen Empires Morgue Thrull and Thrull Surgeon.
There is also an irony about the thrull's thralldom. When they created Thrull Wizards,
"In crafting intelligent Thrulls to assist in sacrifices, Sahr inadvertantly set the stage for the Thrull Rebellion." —Sarpadian Empires, vol. II
The Thrulls bred at a terrifying pace. In the end, they overwhelmed the Order of the Ebon Hand.
Like all the empires described in the Fallen Empires set, the Order of the Ebon Hand was destroyed--but not by their historic enemies (the Icatian Order of Leitbur); no, they were wiped out by their own thrull creations. Despite the best efforts of the Order's counterinsurgency,
Necrites killed Jherana Rure, ending the counterinsurgency.
So the thrulls did not remain the Order's thralls forever.
According to Mark Rosewater, head designer of Magic: The Gathering, thrulls are a creature unique to Magic. They did not originate in any mythology or previous fantasy franchise.
drewishgoy asked: Are the thrulls from another mythology? I always thought they were unique to Magic.
Rosewater: No, they’re a Magic creation.
As Buzz wrote in their answer, the word is very similar to thrall, making that the most likely origin of the word.